Gallium nitride based compound semiconductor light-emitting device and manufacturing method therefor

ABSTRACT

Disclosed are a GaN based compound semiconductor light emitting diode (LED) and a manufacturing method therefore. In the LED, a multi-layer epitaxial structure including an active layer is formed over a substrate, and a light transmissive impurity doped metal oxide which may be formed over a Ni/Au layer is used as a light extraction layer while the Ni/Au layer is taken as an ohmic contact layer between the light extraction layer and the multi-layer epitaxial structure. Then, an n-type metal electrode is disposed over an exposing region of an n-type semiconductor and a p-type metal electrode over the light extraction layer. The LED is thus formed.

BACKGROUND OF THE MENTION

[0001] 1. Field of the invention

[0002] The present invention relates to a GaN based compoundsemiconductor light-emitting device (LED) and a manufacturing methodtherefor, and particularly to a GaN based compound semiconductorlight-emitting device (LED) with better light transparency and amanufacturing method therefor.

[0003] 2. Description of Related Art

[0004] A light-emitting diode (LED) has been generally known as asemiconductor device with ability to emitting light, which has beenwidely used in digital watches, calculators, communications and otherareas, such as mobile phone and some appliances. Recently, variousefforts and attempts have shifted to use LEDs in more ordinary humanliving, such as large panels, traffic lights and illuminationfacilities. However, in marching into a brand new illuminating era withthe current illumination facilities replaced with LEDs, the luminousefficiency of an LED remains a big issue, which has been challengingthose skilled in the art for many years. Therefore, many developmentsand researches have been thrown in to improvement of luminous efficiencyof LEDs, and red, green, blue and white colored lights are alike.

[0005] As is well understood to those skilled in the art, LEDs areproduced based on some semiconductor materials, especially GaN-basedcompound semiconductor materials, and emit lights by virtue of thebehaviors aroused in the semiconductor materials in the presence of anapplied electrical bias.

[0006] In particular, an LED is generally composed of some Group III-V(or Group II-VI, although rarely given forth) compound semiconductors.In principle, an LED is basically a well-known p-n junction structureddevice, i.e., a device having a p region, an n region and a depletionregion therebetween. Upon a forward-biased voltage or current biasapplied, the majority of the carriers in the p or n regions driftrespectively towards the other region through the depletion region inthe device due to the energy equilibrium principle and a current isaccounted for, in addition to the general thermal effects. When someelectrons and holes in the device jumped into a higher value of energyband with the aid of electrical and thermal energy, the electrons andthe holes recombine there and then give off lights when they randomlyfall back to a previous lower energy state (turning from an unsteadystate to a steady state) owing to thermal equilibrium principle, i.e.spontaneous emission. Besides the p-n Junction, in a typical and basicsuch device structure comprise also other components, such as asubstrate, a buffer layer, a transparent layer (TCL) and electrodes. Inachieving a high luminous efficiency LED, each component and theirmutual relationship in the device structure are generally to beconsidered.

[0007] In a typical LED in which the produced light is emitted upward(through the overlaying epitaxy structure), TCL is a layer coated on anLED structure and below a p-type electrode of the LED structure. Sincethe p-type electrode is normally not transparent or not transparentenough and will have blockage on the emitted light to a user's eyes, thep-type electrode should be sized and disposed at a limited portion onthe underlying layer contact therewith. However, the electrical forcelines resulted from between the p-type electrode and an n-type electrodemay not uniformly distribute in the p-n structure in the device. Hence,the electrical charges provided by the applied electrical bias may notefficiently and uniformly stimulate the p-n structure, which is thesource of light generation. Further, the p-type electrode is inheredwith poor immobility as compared to that of the n-type electrode andthus the stimulation efficiency of the electric bias on the device maynot be satisfactory. A thin TCL is in this occasion introduced over thetoppest layer of the device (in fact, below the p-type electrode). TheTCL is a transparent material to a light generated from the device andequipped with ability of electricity conduction. Once an electric biasis fed from the p-type electrode, the corresponding charges will spreaduniformly in the p-n structure with an aid of the TCL underlying thep-type electrode and the poor stimulation efficiency of the electricbias slay be overcome. In this regard, a TCL is a layer indispensable toan LED structure.

[0008] In a prior art, a Ni/Au material (with the Ni layer at the lowerand the Au layer thereon) is used as the TCL in the GaN basedlight-emitting device in achieving an improved light emitting device.However, Ni/Au is not a material with good light transparency and shouldthus be made considerably thin, about 0.005-0.2 It m. On the other hand,according to the critical angle theory, TCL should possess suitablethickness and will then facilitate extraction of the generated light outof the device. Further, too thin a Ni/Au layer will not exhibit a goodohmic contact characteristic. Therefore, Ni/Au material may not be themost appropriate choice for an LED in terms of light transparency andextraction owing to the thickness issue. Further, since Ni/Au as the TCLin such a GaN based light emitting device may not be formed with morefacets by use of a surface treatment under the thickness 0.005-0.2 μm ofthe Ni/Au layer, the Ni/Au layer based light extraction stands littlepossibility to be promoted.

[0009] In view of the foregoing problems, it is needed to set forth aGaN based compound semiconductor LED that really provides an improvedTCL. To this end, the inventors of the present invention provide hereina GaN based compound semiconductor LED with a TCL other than Ni/Au andmay achieve better light transparency and extraction characteristics.

SUMMARY OF THE INVENTION

[0010] It is therefore an object of the present invention to provide aGaN based compound semiconductor light emitting device (LED) which has abetter transparent contact layer (TCL), may be made bulky andfacet-rich, and thus has a higher light extraction characteristic, and acorresponding manufacturing method.

[0011] To achieve the object of the present invention, an impurity dopedmetal oxide is used as the TCL of the LED, instead of Ni/Au materialused in the state of the art. In a preferred embodiment, the impuritydoped metal oxide may be an impurity doped ZnO based layer. When thedoped ZnO based layer is thick enough, the surface thereof may besubject to a surface treatment so that facets thereon may be made more.

[0012] With the inventive GaN based compound semiconductor LED having animpurity doped metal oxide as the TCL and its manufacturing method, theobtained light extraction efficiency is enhanced.

[0013] In the inventive LED structure, the constituent materialscomprise: a substrate, a multi-layer epitaxial structure, a lightextraction layer, an n-type electrode and a p-type electrode. In themulti-layer epitaxial structure, there include a buffer layer, a firstsemiconductor layer, a light generating layer and a second semiconductorlayer.

[0014] A manufacturing method for the inventive LED comprises: (a)forming an n-GaN based layer over a substrate; (b) forming amulti-quantum well (MQV) active layer over the n-GaN based layer; (c)forming a p-GaN based layer over the MQW layer and etching away aportion of the n-GaN layer, MQW active layer and p-GaN layer, whereby anexposing region is formed on the n-GaN layer; (d) forming an impuritydoped metal oxide layer as a light extraction layer over the p-GaN basedlayer; and (e) forming an n-type electrode over an exposing region afterthe etching of the n-GaN based layer, the MQW active layer and the p-GaNlayer and forming a p-type electrode over the light extraction layer. Ina preferred embodiment, the doped metal oxide layer is an Al-dopedZnO-based layer.

[0015] Owing to the large bandgaps of some metal oxides such as ZnO, theLED with a TCL composed of such metal oxides exhibiting better lighttransparency and extraction is thus achieved;

[0016] Additionally, the LED according to the present invention alsoincludes at least the following advantages: bulky light extraction layerand the corresponding light extraction efficiency, surface treated lightextraction layer with more facets and the corresponding lightextraction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] To better understand the other features, technical concepts andobjects of the present invention, one may clearly read the descriptionof the following preferred embodiment and the accompanying drawings, inwhich:

[0018]FIG. 1 depicts schematically a manufacturing method of a preferredembodiment according to the present invention;

[0019]FIG. 2 is a schematically perspective diagram of a light-emittingdevice of a preferred embodiment according to the present invention;

[0020]FIG. 3 depicts schematically a structure of a light-emittingdevice of a preferred embodiment according to the present invention;

[0021]FIG. 4 depicts schematically energy the bandgaps of a ZnO and ap-GaN materials;

[0022]FIG. 5 depicts schematically light extraction of a light-emittingdevice;

[0023]FIG. 6 depicts schematically a manufacturing method of anotherembodiment according to the present invention;

[0024]FIG. 7 and FIG. 8 depict schematically a surface treatment of alight extraction layer;

[0025]FIG. 9 depicts schematically light extraction from particularlytextured area;

[0026]FIG. 10 and FIG. 11 depict schematically a particularly texturedarea of another embodiment according to the present invention;

[0027]FIG. 12 depicts schematically a method of a second embodimentaccording to the present invention;

[0028]FIG. 13 depicts schematically a device of a second embodimentaccording to the present invention;

[0029]FIG. 14 depicts schematically another example of a second methodembodiment according to the present invention;

[0030]FIG. 15 depicts schematically a method of a third embodimentaccording to the present invention;

[0031]FIG. 16 depicts schematically a device of a third embodimentaccording to the present invention;

[0032]FIG. 17 depicts schematically another example of a third methodembodiment according to the present invention;

[0033]FIG. 18 depicts schematically a method of a fourth embodimentaccording to the present invention;

[0034]FIG. 19 depicts schematically a device of a fourth embodimentaccording to the present invention; and

[0035]FIG. 20 depicts schematically anther example of a fourth methodembodiment according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0036] In a preferred (first) embodiment of an LED of the presentinvention schematically shown in FIGS. 1 through 3, the LED is includedwith an impurity doped ZDO based layer at the toppest thereof (but undera p-type electrode in the LED). The doped ZnO based layer is formed overa multi-layer epitaxial structure and has a better lighttransmissibility and a suitable thickness, entitling itself to betterlight extraction for the LED. Specifically, the method and the LEDstructure are described in FIGS. 1 and 2 respectively and each stepthereof will be first explained as follows accompanying with its elementlabels.

[0037] Step 1: forming an n-GaN based epitaxial layer 21 over asubstrate 10. The substrate 10 may be a sapphire or SiC and have athickness of 300-450 μm, The substrate 10 may be first formed with abuffer layer 22 at an upper surface 11 thereof, and then formed overwith the n-GaN based epitaxial layer 21 having a thickness of 2-6 μm.The buffer layer may be composed of some layers, such as a coarse grainnucleation layer made of GaN and an undoped GaN layer. The nucleationlayer is a low temperature layer, i.e. formed under a low temperaturecondition, and has a thickness of 30-500 Å and will be referred to as anLT-GaN layer herein. The undoped GaN is a high temperature layer and hasa thickness of 0.5-6 μm, and will be named as an HT-GAN layer here.These buffer layers may be formed by molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD) and some other suitabletechnologies, currently in existence or set forth in the future.

[0038] Step 2: forming a multi-quantum well (MQW) active layer 23 overthe n-GaN based layer 21. As generally known, an MQW layer is amulti-layered structure and used to enhance possibility of recombinationof holes and electrons in the p-and-n junction structure of the LED. Inthe present invention, the thickness and layer number of the MQW layermay be carefully chosen so that the MQW layer may efficiently increaselight generating efficiency. In addition, the active layer 23 may beserved by an AlGaInN based compound semiconductor epitaxial layer.

[0039] Step 3: forming a p-GaN based epitaxial layer 25 over the MQWactive layer 23 and etching away a portion of the n-GaN based layer 21,the MQW active layer 23 and the p-GaN based layer 25 whereby an exposingregion 21 a is formed on the n-GaN based layer 21, wherein the p-GaNbased epitaxial layer 25 may be such as p-GaN, p-InGaN and p-AlInGaNlayers and have a thickness of 0.2-0.5 μm. It is noted that the etchingmay be performed with chlorine plasma dry etching, etc.

[0040] Step 4: forming a doped ZnO based layer 31 over the remainingp-GaN based layer 25 after said etching. Since the layer 31 is providedat the toppest of the LED structure for light exiting excepted for ap-electrode 50, the layer is also termed as a window layer. Thethickness of this doped ZnO based layer may be arranged between 50 Å and50 μm. Preferably, the thickness is made larger than 1 μm, and thereason will be stated in the following related to the LED structure. Ina prefer embodiment, the impurity doped in the doped ZnO based layer 31may be a p-type impurity or an n-type impurity, and the p-type impuritymay at least be Al. Once the activation issue of the impurity doped ZnObased layer 31 may be overcome, all Group-III elements may be thesuitable dopants.

[0041] Step 5: forming a p-type electrode 50 over the doped ZnO basedlayer 31 and forming an n-type electrode 40 over said exposing region 21a of said n-GaN based layer 21.

[0042] As far as formation of the doped metal oxide layer ZnO isconcerned, either of self-texturing by sputtering, physical vapordeposition, ion plating, pulsed laser evaporation chemical vapordeposition and molecular bean epitaxy and other suitable technologiesmay be employed.

[0043] In fact, to completely form a marketed LED, some treatments arealso needed comprising wire bonding and packaging molded by such asepoxy (not shown). Since the wire bonding and packaging technology iswell known to those persons skilled in the art, they are omitted in thedetailed descriptions, for simplicity, of the inventive LED for both itsstructure and method.

[0044] The following is dedicated to the inventive LED structure.Referring to FIG. 3, the LED structure 12, corresponding to the abovemanufacturing method, includes a substrate 10, a multi-layer epitaxialstructure 20, a first semiconductor layer 24, a light generating layer26 and a second semiconductor Specifically, said substrate 10 is made ofsapphire or SiC and has a thickness of 300-450 μm. The buffer layer 22is a multi-layer structure such as a double layered one. In this case,the buffer layer 22 is composed of an LT-GaN layer and an HT-GaN layer,as has been explained in the preferred method embodiment, formed over anupper surface 11 of the substrate 10.

[0045] The first semiconductor layer 24 is an n-GaN based III-V groupcompound semiconductor, which may range from 2 to 6 μm in thickness. Thelight generating layer 26 is an. GaN based III-V group compoundsemiconductor, generally known as an active layer, and may be a GaNmulti quantum well (MQW) or an InGaN multi-quantum well. The secondsemiconductor layer 28 is a p-type GaN based 111-V group compoundsemiconductor, which may be such as p-GaN, p-InGaN and p-AlInGaN.

[0046] The light extraction layer 30 is made of an impurity doped metaloxide, which is light transmissive and formed over the secondsemiconductor layer 28. As an example and a preferred embodiment, thelight extraction layer 30 is composed of doped ZnO. The n-type electrode40 is disposed over an exposing region 24 a of the first semiconductorlayer 24 and the p-type 50 over the light extraction layer 30.

[0047] With the improved doped ZnO light extraction layer 30, the lightgenerated from the active layer 26 in the inventive LED is morepenetratable through when it encounters the layer 30 in the course ofgoing out of the LED. Further, because the light extraction layer 30 maybe subject to surface treatment to have the surface roughened and someform textured, the surface of the light extraction layer may obtain morefacets and thus the light extracted to a user's eyes may be increased.

[0048] Here, there are some descriptions supplemented to the aboveembodiment. The light generating layer 26, i.e., active layer, mayalternatively be a single AlGaInN III-V group compound semiconductorlayer. The light extraction layer 30 may further be other metal oxideswith impurity doped, such as impurity doped In_(x)Zn_(1-x)O, impuritydoped Sn_(x)Zn_(1-x)O and In_(x)Sn_(y)Zn_(1-x-y)O, one having an indexof refraction of at least 1.5, one being n-type conductive or p-typeconductive, one doped with a rare earth element, or one having atransmissive range of a light with a wavelength of 400-700 nm.

[0049] The afro-mentioned is the preferred embodiment of the presentinvention, which may be easily modified by those persons skilled in theart. Hence, devices or methods deduced with reference to the disclosedone are deemed to fall within the spirit of the present invention. Forexample, although the description of the LED and its manufacturingmethod of the present invention are limited to the Group III-V compoundsemiconductor based LED, the inventive impurity doped metal oxide lightextraction layer may be employed onto the Group II-VI group compoundsemiconductor based LED as long as the lattice matching issue on suchLED may not be problematic.

[0050] The following will be made to the reason that doped ZnO may bemore appropriate to serve as the light extraction layer as compared tothe prior light extraction layer in an LED. Referring to FIG. 4, thebandgap energy B1 of ZnO is approximately 3.4 eV, and the bandgap B2 ofp-GaN is also near 3.4 eV. Owing to the small bandgap energy offset,lattice matching will not be an issue to their bonding and the operatingvoltage will not be too large. In this regard, bonding the impuritydoped ZnO extraction layer over the p-GaN layer is well possible. Fornumerical information, GaN has a lattice constant of about 3.189 Å, ZnOof about 3.24 Å, and sapphire of about 4.758 Å.

[0051] In an LED device, as generally known, only those lights withemitting angles smaller than the critical angle may really extract outof the device, schematically shown in FIG. 5. In response to this, alight extraction layer with a suitable thickness may be benefited withincreased light extraction amount. As the example of the presentinvention, the light extraction layer 30 has a thickness of at least 1μm, which makes the lights emitted from the active layer easier topenetrate through the surface 301 and the sides 302 and thus enhance thelight extraction efficiency.

[0052] Referring to FIG. 6, since the light extraction layer 30 in thepresent invention may be ranged between about 50 Å-50 μm in thickness,the layer 30 may be made thick enough to be bulky one. When thethickness of the light extraction layer 30 is at least 1 μm, the abovemethod embodiment may further include a step, Step 6, i.e., subjectingan exposing surface of the doped ZnO based layer 30 (i.e., the portionof the light extraction layer 30 other than the portion thereofcontacted with the p-type electrode 50) to a surface treatment. With thesurface treatment, the surface of the layer 30 may be further roughenedso that more facets may be formed thereover. With the facet-richsurface, light extraction efficiency may be considerably increased.

[0053] Proceeding to the above paragraph, the light extraction layer 30may be further subject to particular texturization and obtained withtextured surface. Similar to the recitation of the above paragraph,texturization treatment may also increase facet number of the lightextraction layer 30. And the goal to increasing light extraction may beachieved. The particular textured surface may be in the form of a cone,comprising one with a triangular 303 bottom shown in FIG. 7 and one witha rectangular bottom 305 shown in FIG. 8, and may be other geometricalcones, which may either be applied onto the light extraction layer 30.

[0054] Referring to FIG. 0.9, that light extraction may be benefitedfrom the roughened or textured surface of the light extraction layer 30is schematically explained therein. For a flat light extraction layer, aportion of the emitted light is reflected by the flat surface. However,the two facets 302 may provide the emitted light with several times ofreflection and the extracted portion of the emitted light may well beincreased.

[0055]FIGS. 10 and 11 are planar diagram and partial perspective diagramrespectively for illustration of another textured surface embodiment. Inthe two figures, the textured portion of the surface may further includea plurality of recesses 307, which may be triangular, rectangular,diamond, polygonal or other arrangements. Between recesses 307 is adistance of a suitable value, which is provided for conductive path ofcurrent.

[0056] Referring to FIGS. 12 and 13, which illustrate a secondembodiment of the present invention. In the embodiment, an impuritydoped In_(x)Zn_(1-x)O is used as the light extraction layer 32, which isgrown to a suitable thickness over the multi-layer structure asmentioned in the first embodiment, wherein 0≦X≦1. The steps used in thisembodiment are generally similar to those in the preferred embodimentexcept for the step, Step 4 a. Step 4 a is a step of forming an impuritydoped In_(x)Z_(1-x)O based layer over the p-GaN layer.

[0057] Referring to FIG. 14, the second embodiment according to thepresent invention may further comprise a step, Step Sa, as compared tothat in FIG. 12: subjecting the doped In_(x)Z_(1-x)O based layer to asurface treatment. In the step, the treatment is applied only to theregion of the layer 32 not covered by the p-type electrode 50.Similarly, the increase of facets on the layer 32 may efficientlyenhance light extraction.

[0058] Referring to FIGS. 15 and 16, which illustrate a third embodimentof the present invention. In the embodiment, an impurity dopedSn_(x)Zn_(1-x)O 33 is used as the light extraction layer, which is grownto a suitable thickness over the multi-layer structure as mentioned inthe first embodiment, wherein 0≦X≦1. The steps used in this embodimentare generally similar to those in the preferred embodiment except forthe step, Step 4 b. Step 4 b is a step of forming an impurity dopedSn_(x)Zn_(1-x)O based layer over the etched p-GaN layer.

[0059] Referring to FIG. 17, the third embodiment according to thepresent invention may further comprise a step, Step 5 b: subjecting theimpurity doped Sn_(x)Zn_(1-x)O based layer to a surface treatment. Inthis step, the treatment is applied only to the region of the layer 33not covered by the p-type electrode 50. Similarly, the increase offacets on the layer 33 may efficiently enhance light extraction.

[0060] Referring to FIGS. 18 and 19, which illustrate a fourthembodiment of the present invention. In the embodiment, an impuritydoped In_(x)Sn_(y)Zn_(1-x-y)O is used as the light extraction layer 34,which is grown to a suitable thickness over a multi-layer structure asmentioned in the first embodiment, wherein 0≦X≦1, 0≦Y≦1 and 0≦X+Y≦1. Thesteps used in this embodiment are generally similar to those in thepreferred embodiment except for a step, Step 4 c. Step 4 c is a step offorming an impurity doped In_(x)Sn_(y)Zn_(1-x-y)O based layer over theetched p-GaN layer 25.

[0061] Referring to FIG. 20, the fourth embodiment according to thepresent invention may further comprise a step, Step 5 c: subjecting theimpurity doped In_(x)Sn_(y)Zn_(1-x-y)O based layer to a surfacetreatment. In this step, the treatment is applied only to the region ofthe layer 34 not covered by the p-type electrode 50. Similarly, theincrease of facets on the layer 34 may efficiently enhance lightextraction. If the exposing surface of the above mentioned structure isthin enough, the exposing surface can dope no Zno as well.

[0062] While the invention has been described by way of examples and interms of preferred embodiments, it is to be understood that theinvention is not limited thereto. On the contrary, it is intended tocover various modifications and similar arrangements and procedures, andthe scope of the appended claims therefore should be accorded thebroadest interpretation so as to encompass all such modifications andsimilar arrangements and procedures.

What is claimed is:
 1. A method for manufacturing a GaN based compoundsemiconductor light-emitting device, comprising the steps of: (a)forming an n-GaN based layer over a substrate after a buffer layer isformed over said substrate; (b) forming a multi-quantum well (MQW)active layer over said n-GaN based layer; (c) forming a p-GaN basedlayer over said MQW layer and etching away a portion of said n-GaN, MQWactive and p-GaN layers whereby an exposing region is formed on saidn-GaN based layer and an exposing surface is formed on said p-GaN basedlayer; and (d) forming an impurity doped ZnO based layer as a lightextraction layer over said exposing surface after said etching of saidn-GaN layer, MQW active layer and p-GaN based layers, wherein said dopedZnO based layer is doped so that said doped ZnO based layer is lighttransparent and conductive; and (e) forming a p-type electrode over saidlight extraction layer after said etching and forming an n-typeelectrode over said exposing region of said n-GaN layer.
 2. According tothe method in claim 1, wherein said doped ZnO based layer comprises ZnO,Sn_(x)Zn_(1-x)O, In_(x)Z_(1-x)O and In_(x)Sn_(y)Z_(1-x-y)O wherein0≦X≦1, 0≦Y≦1 and 0≦X+Y≦1, and wherein said impurity comprises p-type andn-type impurities.
 3. According to the method in claim 2, wherein saidp-type impurities comprises Al.
 4. According to the method in claim 1,wherein said light extraction layer has a thickness of 50 Å to 50 μm. 5.According to the method in claim 1, wherein said substrate may be lighttransmissive or opaque and comprises sapphire, Si or SiC.
 6. Accordingto the method in claim 1, wherein said doped ZnO based layer is at leasttransparent to a light having a wavelength of 400-700 nm.
 7. The methodaccording to claim 4, wherein when said light extraction layer has athickness being at least 1 μm, said method further comprises a stepbetween said steps of (d) and (e) or succeeding to said step (e): (f)subjecting said doped ZnO based layer to a surface treatment byroughening or particularly texturizing whereby a plurality of facets areformed on said doped ZnO based layer.
 8. A GaN based compoundsemiconductor light-emitting device, comprising: a substrate; amulti-layer epitaxial structure comprising: a buffer layer being anIT-GAN/HT-GaN layer formed over an upper surface of said substrate,wherein said LT-GaN is a low temperature layer first formed over saidsubstrate, and said HT-GaN layer is a high temperature layer then formedover said LT-GaN layer; a first semiconductor layer being an n-GaN basedcompound semiconductor layer formed over said buffer layer; a lightgenerating layer being a GaN based compound semiconductor active layercomprising a GaN multi-layer quantum well (MQW) layer; and a secondsemiconductor layer being a p-GaN based compound semiconductor formedover said light generating layer; a light extraction layer being animpurity doped metal oxide transmissive to light and formed over saidsecond semiconductor layer and comprising impurity doped ZnO basedlayer; an n-type metal electrode disposed over an exposing region ofsaid first semiconductor layer; and a p-type metal electrode disposedover said light extraction layer.
 9. According to the light-emittingdevice in claim 8, wherein said substrate has a thickness of 300-450 μm,said LT-GaN has a thickness of 30-500 Å, said HT-GaN has a thickness of0.5-6 μm, said first semiconductor has a thickness of 2-6 μm and saidsecond semiconductor layer has a thickness of 0.2-0.5 μm, and saidsecond semiconductor layer is selected from a group consisting of ap-GaN, a p-InGaN and a p-AlInGaN epitaxial layers.
 10. According to thelight-emitting device in claim 8, wherein said light generating layerfurther comprises an InGaN/GaN MQW layer.
 11. According to thelight-emitting device in claim 8, wherein said light generating layerfurther comprises an AlGaInN based compound semiconductor epitaxiallayer.
 12. According to the light-emitting device in claim 8, whereinsaid light extraction layer further comprises a layer selected from agroup consisting of an impurity doped In_(x)Zn_(1-x)O impurity dopedmetal oxide layer, an impurity doped Sn_(x)Zn_(1-x)O impurity dopedmetal oxide, wherein 0≦X≦1, and an In_(x)Sn_(y)Zn_(1-x-y)O impuritydoped metal oxide layer, wherein 0≦X≦1, 0≦Y≦1 and 0≦X+Y≦1, and saidimpurity comprises a p-type impurity and an n-impurity.
 13. According tothe light-emitting device in claim 8, wherein said light extractionlayer further comprises an impurity doped metal oxide having an index ofretraction of at least 1.5.
 14. According to the light-emitting devicein claim 12, wherein said p-type impurity comprises Al.
 15. According tothe light-emitting device in claim 8, wherein said light extractionlayer further comprises a metal oxide doped with a rare earth element.16. According to the light-emitting device in claim 8, wherein saidlight extraction layer comprises an impurity doped metal oxide having atransmissive range for a light having a wavelength of 400 to 700 nm. 17.According to the light-emitting device in claim 8, wherein said lightextraction layer has a thickness of 50 Å to 50 μm.
 18. According to thelight-emitting device in claim 17, wherein when said light extractionlayer has a thickness of at least 1 μm, said light extraction layer hasa roughened or particularly textured surface comprising a plurality offacets.
 19. According to the light-emitting device in claim 18, whereinsaid particularly textured surface comprises a cone-shaped texturedsurface, wherein said cone comprises a cone with a triangular bottom, acone with a rectangular bottom and a cone with any other shaped bottom.20. According to the light-emitting device in claim 19, wherein saidparticularly textured surface comprising a plurality of recesses, eachof the recesses has a suitable distance with an adjacent recess as aconductive path and arranged in a particular form selected from a groupconsisting of triangular, rectangular, polygonal, diamond and any othergeometrical forms.
 21. A method for manufacturing a GaN based compoundsemiconductor light-emitting device: forming a multi-layer epitaxialstructure over a substrate, wherein said multi-layer epitaxial structureincludes a p-type semiconductor layer, an active layer and an n-typesemiconductor layer; forming an impurity doped metal oxide having asuitable thickness and a light transmissibility over said multi-layerepitaxial structure as a light extraction layer; and disposing an n-typeelectrode over an exposing region of said n-type semiconductor layer anddisposing a p-type electrode over said light extraction layer. 22.According to the method in claim 21, wherein said impurity doped metaloxide layer is selected from a group consisting of an impurity doped ZnOlayer, an impurity doped In_(x)Zn_(1-x)O layer, an impurity dopedSn_(x)Zn_(1-x)O layer and an In_(x)Sn_(y)Zn_(1-x-y)O layer, wherein0≦X≦1, 0≦Y≦1 and 0≦X+Y≦1.
 23. According to the method in claim 21,wherein said impurity doped metal oxide layer is formed through atechnology selected from a group consisting of self-texturing bysputtering, physical vapor deposition, ion plating, pulsed laserevaporation chemical vapor deposition and molecular beam epitaxytechnologies.
 24. According to the method in claim 21, wherein saidimpurity comprises a p-type impurity and an n-type impurity. 25.According to the method in claim 24, wherein said p-type impuritycomprises Al.